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Know When Consumer Unit Replacement
Must Not Be Neglected

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Consumer Unit
Consumer Unit

What is a Consumer Unit?

Also referred to as a fuse box, fuse board, or distribution board, a consumer unit installed in your property plays a vital role in controlling and distributing the home’s electrical supply. To put it more precisely, it is the spot where electricity enters before getting circulated to other rooms. All takes place via a collection of unique components, most of which work without you having to exert yourself. The main electrical power moves through the electrical metre and is distributed to different electrical circuits within the property.

What works for you while you consider consumer replacement can best be elaborated by breaking down the information into more manageable units. Our guide will cover the following sections:

  • How a consumer unit works
  • When should you replace a consumer unit
  • Which is the best consumer unit
  • Basic guidelines on the consumer unit

How Does a Consumer Unit Work?

Several components contribute to a consumer unit’s working:

Main Switch

As the name implies, this switch is responsible for providing electricity to the consumer unit from the meter. Switching off the consumer unit will render it disconnected from the power supply and unable to distribute electricity to your property. It tends to be the only switch in your fuse board that you can manually turn off and on. If, for instance, you face any electrical issue at home or need to undertake any repairs, you will turn off the main switch to disconnect it from the electricity supply.

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Residual Current Device (RCD) is a switch that monitors all electrical currents in your property. They help stop electric shocks and detect faults that can cause a fire. Just when they notice an imbalance in the power flow, the switches automatically turn off, an occurrence known as tripping. As per July 2008 Wiring Regulations, all new wired or rewired premises mandate an RCD for protection purposes.

It is a life-saving device to protect you from suffering a fatal electric shock if you touch something like a bare wire. Once it detects electric flow in an unintended path, such as through the human body that has touched a live part, RCD immediately will switch off the circuit to prevent any serious harm. Also giving protection against electrical fires, RCDs provide the level of safety that standard fuses and circuit-breakers do not offer.


The Miniature Circuit Breaker operates automatically to keep an electrical circuit from any damage caused by excessive current. They trip in the case of an overload or short circuit to prevent electrical faults and equipment breakdown. 


Residual Current Breaker with Overcurrent integrates the RCB and MCB usage. It is an essential part as it stops overload, overcurrents, and electric shocks, as well as tripping.


The Surge Protection Device offers a protective layer over the electrical system and any appliance that you connect to the system. During your fuse board installation, your electrician will examine if an SPD is needed.


Beneath the main switch are interconnecting cables to supply power to each RCD that has its own neutral terminal bar. Neutrals from one RCD mustn’t be mixed up with those of the other; otherwise, random RCD tripping will occur. 


This solid copper bar below the MCBs transports the electricity to each MCB. If each MCB is on, the current will flow through the final circuit connected to the top terminal of the MCB.

The current passes through the circuit, around your property, to sockets, lights, etc. If the current exceeds in the MCB, the MCB will trip. And in case of a current imbalance in any circuit covered by the RCD (usually 30mA), the RCD will trip.

When Should You Replace a Consumer Unit?

Whether or not to change your consumer unit depends on several factors:

If the Electrician Installation Condition Report Says So

You might have got an electrical installation condition report carried out only to know that it recommends you get your consumer unit or fuse box replaced. If you want to know what brought them to suggest this, you may discuss it with the electrician who ran the test and examined your unit. 

Consumer Unit

If You Have a Fuse Box

If you have got a fuse board, in which fuse wire instead of MCBs protect the circuits, you should know some crucial differences between the consumer unit and fuse box:

  • There will be an extended period of disconnection time for the type of circuit overload protection. If a lot of current is passing through the circuits, for instance, because of several electric heaters turned on at one circuit, the fuse wire will blow, or MCB tripped, to keep the cable from overheating and ultimately melting.
  • It is difficult and potentially risky to replace the blown fuse wire. A fuse wire might blow on a dark winter evening resulting in a disconnected lighting circuit. You will then remove the cover on a few fuse boards to reach the fuse, exposing the live parts. You may later fiddle with the screw fuse holder while threading the fuse wire into the fuse holder, all done kneeling on your knees in the dark.
  • There will likely be no RCD protection on a fuse board, which means that you and your family are more vulnerable to electric shock during an electrical fault. The fuse (or MCB) secures the cable while the RCD protects you during installation and touching of live parts. In that case, you are a part of the electrical system while some current passes through you to earth. This causes an imbalance between the current flowing from the supply and that flowing back, something detected by the RCD, which subsequently trips off.
  • Some old fuse boards might carry an old-fashioned earth leakage device situated before the fuse board. Yet it does not meet today’s higher standards, given their deterioration over time and delayed tripping off.

You may Not have Alternative Ways to Accommodate New Circuits

If, for instance, you get a new garage or outhouse constructed, you will require a new consumer unit. This way is preferable rather than increasing the number of existing circuits for the same consumer unit. 

Other Situations That Require a Consumer Unit Upgrade

  • MCBs Are Worn Out
  • Consumer Unit May Be Damaged, is Not Safely Installed, or Has Holes Causing Potential Electric Shocks
  • You Want Additional Circuits and Installations Complying With the Latest Regulations

Which is the Best Consumer Unit?

The answer to this depends on the following factors:

  • Where the consumer unit will be situated
  • How many circuits it will serve
  • Whether you want a minimal disruption in the case of a circuit fault – i.e. only one circuit tripping off instead of many
  • Whether you prefer quality or budget
  • Whether you require additional protection such as SPDs and AFDDs

Contact us to get your queries addressed. We have the answers to your questions.

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Electric Technician Job

Basic Guidelines on the Consumer Unit

Purchase the Most Expensive Unit You Can Afford:

A costly consumer unit comes with better quality and safety. Superior components in the board, such as the MCBs and RCDs, can save your life. And there is no better alternative to life-saving measures.

Consider More Circuits Than You Have:

Ensure you have some spare routes on the board. For instance, if the house uses 8 circuits, consider installing a 10-way board. Your contingency plan will work when, for example, you get a new cabin built in your garden.

What is Better – MCB or RCBO?

Modern consumer units come in two forms – Split load or dual RCD consumer units; RCBO consumer units.

A split load or dual RCD consumer unit carries a main switch to disconnect power from the entire consumer unit and 2 RCDs, each isolating power to half of the circuits. This means in the case of tripping off of one of the RCDs, all the circuits and MCBs it protects will lose power, causing much disruption.

On the other hand, the RCBO consumer unit also has a main switch, but an RCBO protects each circuit (which essentially is an RCB and MCB in one unit). If a fault occurs, only the circuit with the fault gets its RCBO tripped off, thus causing minimal disruption.

Therefore, RCBO consumer units are more expensive but a much better option. 

Consumer Unit without RCD Protection:

In certain instances, a consumer unit without RCD protection can be used. One such application may be a shed needing sockets and a lighting circuit drawn from an armoured cable, say from a circuit on the consumer unit of the house. The consumer unit in the shed will not require another RCD if the supply circuit on the main consumer unit is RCD protected and the correct disconnection times are met.

Consumer Unit with SPD and Consumer Unit with AFDD:

With the progressive addition of wiring regulations, electrical safety is furthered through more developments done in the field. Two such recent additions are Surge Protection Devices (SPDs) and Arc Full Detection Devices (AFDDs).

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